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The Bluebird and the House Wren

Hello Birders, Yesterday morning I found five nests in the space of an hour along the valley oak-lined dirt road into Round Mountain Ranch. The first was a

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, May 31, 2013

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Hello Birders,

Yesterday morning I found five nests in the space of an hour along the valley oak-lined dirt road into Round Mountain Ranch.

The first was a house finch nest. It was completely concealed in a long festoon of lace lichen (Ramalina menziesii) several feet down from a valley oak branch and about eight feet above the road. About six feet away, and at the same level, a house wren went in and out of a rotted-out cavity where a branch had broken off from the trunk. I didn't keep track of whether one or two birds were coming and going, but a male was singing nearly continuously in the vicinity.

Next I followed the flight of a western kingbird and saw her(?) disappear from sight high up in a valley oak. She was sitting in a nest when I found her with binoculars, and her mate was nearby on a branch. The nest had some blue plastic tarp strands in it.

After walking down the road a bit I watched a house finch disappear into a droopy clump of mistletoe, also about eight feet off the ground, and by climbing the road bank I was able to see a cup nest in the mistletoe.

But the most exciting sighting came next, after I saw a bluebird disappear into and emerge from one of three recently worked holes in a vertical dead branch. "Aha! A bluebird nest to add to my list," naively thought I. Sticking around to watch for a bit, I was soon amazed to see a house wren dart in and out of the same hole.

At first, I thought I must have been mistaken about which hole the bluebird had used, but when the bluebird came back it entered the hole the house wren had just left! This time I was looking through my binoculars, and saw that the bluebird was carrying nest material when it emerged. It zoomed off carrying the dried wild oat seed, heading in the same direction it had gone before. Lying down on the shoulder to save my neck, I kept my binoculars trained on the opening in order not to miss the next installment, which turned out to be even more interesting. The house wren landed in short order on the lip of the opening and, while perched there, reached in to grab nest material with its bill and summarily tossed it to the wind with a flick of its head. It must have done this about seven times before flying away just before the bluebird came back for more.

I suspect the bluebirds had been using the cavity and the house wrens had staged a hostile takeover, possibly destroying bluebird eggs or nestlings in the process, and the bluebirds were attempting to salvage what they could of their nest. (According to Cornell's Birds of North America Online, ornithologists believe that when house wrens destroy the eggs or nestlings of cavity nesting birds of other species, the killing is incidental to their removal of nest material.) It will be interesting to see if the finch nest near the other house wren nest survives, as house wrens are known to puncture the eggs of cup-nesting birds as well as cavity-nesters. There are no good theories about their motivation for that.

Author of Secrets of the Oak Woodlands,
a book about plants and animals that
live among California's oaks. The book
will be published by Heyday in spring of 2014.
Oak habitats support more diversity of life
than any other terrestrial ecosystem in
California.

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